In future wireless communications, a carrier frequency higher than a carrier frequency adopted in a 4th-Generation (4G) communication system may be adopted for communications, such as 28 GHz and 38 GHz, and such a high-frequency channel has shortcomings of higher free transmission loss, high oxygen absorption rate, great influence of rain fade and the like, and seriously influences coverage performance of a high-frequency communication system. However, a carrier frequency corresponding to high-frequency communication has a shorter wavelength, so that more antenna elements may be accommodated on a unit area; and accommodation of more antenna elements means that an antenna gain may be improved by adopting a beamforming method, so that coverage performance of high-frequency communications is ensured.
After a beamforming method is adopted, a transmitter may concentrate transmission energy in a certain direction while there is little or no energy in another direction, that is, each beam has own directivity, as shown in FIG. 1, each beam may only cover terminals in a certain direction, and the transmitter, i.e. a Node B, is required to transmit multiple beams to implement omnidirectional coverage. However, before a Node B establishes a connection with a terminal, the Node B cannot know a position of the terminal, and can also not know channel state information between the Node B and the terminal, so that the Node B does not know which beam may cover the terminal; similarly, the terminal also does not know a direction in which a signal may be sent to cover the Node B. From a previous design concept of a Long Term Evolution (LTE) system, it can be seen that it is necessary to accurately acquire the channel state information between the Node B and the terminal so as to obtain a beamforming weight in the channel state information to achieve a good beamforming effect. For obtaining a better beamforming weight, a receiver, i.e. the terminal, is required to measure and feed back downlink channel state information or weight for a transmitter, i.e. the Node B; and the transmitter, i.e. the Node B, is required to measure and feed back uplink channel state information or weight for the receiver, i.e. the terminal, so that it is ensured that the Node B may send a downlink service by adopting an optimal beam and the terminal may also send an uplink service by adopting an optimal beam. However, under such a condition, when a high carrier frequency is adopted for communications, the Node B cannot cover the terminal by virtue of the optimal beam before obtaining the beamforming weight, so that the terminal cannot perform measurement by virtue of a reference signal sent by the Node B; or, even though the Node B covers the terminal, the terminal cannot reach coverage the same as that of the Node B, so that the Node B cannot acquire a content fed back by the terminal, and the Node B cannot perform beamforming weight selection and normal communications.
Therefore, how to obtain an optimal beam of a corresponding terminal by a Node B is a problem to be solved in high-frequency communications.